Create a Stream processor introspector

Reading from the topology stream NXP-29934 and stream metrics NXP-2933 we can build a representation of the stream processor in a Nuxeo cluster.

This can be done with a computation reading from both streams and that outputs a representation DAG into the KV store with a TTL of ~10min.

This DAG can be exposed with a REST API probably from the management API.

We already have a PUML representation of topology a first attempt could be to output an SVG (or PUML content).

Note that reading from stream metrics ensure to represent only nodes that are alive,